Please refer to FIG. 1, which shows an on-line uninterrupted power supply (UPS) system for three-phase input according to the prior art. The three-phase AC (Alternating current)/DC (Direct current) converter 101 and DC/DC converter 102 together serve as the front input of the inverter 103. While the three-phase power supply 106 is normal, the controlling switch 104 is cut off so that the DC/DC converter 102 does not work and the three-phase AC/DC converter 101 provides direct power for the inverter 103. On the contrary, while the three-phase power supply 106 is abnormal, the controlling switch 104 is turn on so that the DC/DC converter 102 works and the battery 105 with lower energy provides a direct power for the inverter 103. Moreover, the numeral 107 represents the output path of the voltage or current in the on-line UPS system for three-phase input under the normal conditions; the numeral 108 represents the bypass output path of the voltage or current in the on-line UPS system for three-phase output; the numeral 109 represents the output end of the UPS system.
In FIG. 1, the front power supply of the inverter 103 employs the two converter devices of AC/DC and DC/DC. Thus, it has higher cost and lower power density. Please refer to FIG. 2, which shows a topological circuit diagram of an uninterrupted power supply system for three-phase input and single-phase output according to the prior art. In this drawing, ua, ub, uc respectively represent three-phase input power supply; N represents neutral line; ia, ib, ic respectively represent three-phase input current. Meanwhile, the AC/DC and DC/DC converter 201 is mainly composed of rectifying circuits including D1˜D6 rectifying diodes, controlling switch S0, battery 202, inductors L1, L2, switching devices S1, S2, fast recovery diodes D7, D8, input voltages V01, V02, and capacitors C1, C2. Inverter 203 is mainly composed of switching devices S3, S4. Vo represents output voltage of the UPS system for three-phase input and single-phase output.
In the present description, the described switching device can be MOSFET, IGBT, and etc. In FIG. 2, the circuit employs a half-bridge inverter served as output, and employs a power converter integrating AC/DC and DC/DC converting function for the front input of the inverter. While the power supply is normal, the power converter device turns off the controlling switch S0 and achieves the three-phase AC/DC power conversion. However, while the power supply fails, the controlling switch S0 will be turned on so as to achieve the three-phase DC/DC power conversion. This kind of integrated converter can respectively achieve the AC/DC and DC/DC transformation via the same power elements under different conditions. Therefore the utilization rate of the power elements is increased and the cost of the UPS reduced. However, in the integrated converter there is an obvious defect existed that the AC/DC converter almost lacks of the function of power factor correction. While the three-phase power supply is employed, the input current harmonics is quite high and the total harmonic distortion rate is about 30% so that it cannot meet the harmonic requirement of the input current of the electrical devices in different countries. Therefore, the above-mentioned integrated converter still bears great restriction in the application.
In order to overcome the drawbacks in the prior art, an integrated converter having three-phase power factor correction is provided. In the particular design, the integrated converter can achieve a lower input current harmonics to meet different requirements and have the features of high efficiency, high density, low cost, and etc.